DockerCon 2016

Dockerfiles are great. They provide a zero-barrier-to-entry format for
describing a single Docker image which is immediately clear to anyone
reading them. But with that simplicity comes problems that become
apparent as your adoption of Docker gathers pace.

* Dockerfiles can inherit from other docker images, but images are not
Dockerfiles
* Dockerfile provides no built-in mechanism for creating abstractions,
so as usage grows identical or similar instructions can be duplicated
across many files
* The Docker APi exposes a build endpoint, but the API is very course,
taking Dockerfile as the transport rather than exposing the individual
instructions
* Dockerfiles are just that, files. So they can come from anywhere

The one layer per line in a Dockerfile limitation can lead to an
explosion of layers, which fail to take advantage of the promised
space and performance benefits.